Metal degassing apparatus



Dec. zo, 196e C, W. FINKL 3,292,916

METAL DEGAS SING APPARATUS Filed July 22, 1965 4 Sheets-Sheet l BYParker Kaffe/f /lzzo/w/.

Dec.20, 1 966 i C. w. FlNKL 3,292,916

MTAL DEGASSING APPARATUS Filed July 22, 1965 4 Sheets-Sheet 2 IN VENTOR.

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D66. 2o, 1966 C, W, FINKL 3,292,916

METAL DEGASS ING APPARATUS Filed July 227 196.5 l 4 Sheets-Sheet 3 INVEN TOR.

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METAL DEGASSING APPARATUS 4 Sheets-Sheet 4 Filed July 22, 1965 INVENTOR.

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BY par??? (arie/f fzomqyf United States Patent O 3,292,916 METALDEGASSING APPARATUS Charles W. Finkl, Chicago, Ill., assigner to A.Finkl & Sons Co., Chicago, Ill., a corporation of Illinois Filed July22, 1965, Ser. No. 477,083 8 Claims. (Cl. 266-39) This application is acontinuation-impart application of copending application Serial Number108,513, iiled May 8, 1961, now abandoned.

My invention relates to degassing molten metals. It relates particularlyto apparatus which will enable the included gas content in a heat ofmolten metal to be reduced to very low levels within the permissibletemperature drop limitation of the metal. The apparatus enablesreduction of the included gas content to be accomplished by -the use ofvacuum as the sole degassiug agent.

In recent years there has been an increasing demand for higher andhigher quality in all types of steel. Increased ductility, toughness,and transverseA properties have become of particular importance. Myinvention enables increased ductility, toughness, and .transverseproperties to be achieved with little, if any, increase in the cost ofproduction.

It is believed that ductility and toughness are related in some degreeto the included gas content of the metal, particularly hydrogen andoxygen. A large included hydrogen content, for example, results inflaking. A high oxygen content indicates high oxide inclusions. At thepresent time it is thought that flaking, or the presence of cracks, canbe reduced by heat treatment after the metal has been poured. Heattreatment is effective to reduce cracking, but heat treatment does nothave much eiect on ductility.

A second method of increasing ductility and toughness is to degas themolten metal. It is believed that heat treatment can be curtailed whendegassing is employed and it is therefore possible that the overall costof producing the steel will be reduced.

The above comments are particularly pertinent to the production of steelin large quantities. Other problems equally serious face the foundry manwho pours castings from heats on the order of from 1 to 10 tons. Incastings poured from heats of this size, hot tearing is very much aproblem if the included gas content is high. In addition, it is verydesirable to reduce the dirt in castings. By the term dirt I mean oxidesor inclusions which result from the presence of too much hydrogen,nitrogen, and, particularly, oxygen in the metal.

Various methods of treating the molten metal before it is poured intomolds have been proposed. Many of them are impractical due to thespecial equipment needed which is not practical for day in, day outproduction. Other methods require the molten metal to be treated forsuch a length of time between tapping and pouring that the permissibletemperature drop limitatioi'i of the metal is exceeded.

Permissible temperature drop lirni-tation as used i-n this specificationand claims relates to that drop in temperature which can be toleratedbefore the metal is considered too cold for pouring. If a heat of lowalloy steel is tapped at approximately 3,100 degrees F., the permissibletemperature drop limitation expressed in terms of temperature would beon the order of 250 degrees F., depending to some extent on thecomposition of the steel and other factors. Permissible temperature droplimitation may also be expressed in terms of time. When so expressed, itmay be considered to be that length of time elapsing between the timethe steel is tapped until it is so cold as to be unsuitable for teeming.

Accordingly, a primary object of this invention is to 3,292,916 PatentedDec. 20, 1966 "icc provide means for degassing small heats of moltenmetal which will reduce dirt and the tendency to hot tear, and provideincreased ductility, toughness, and transverse strength in the finalproduct, particularly castings.

Another object is to provide an apparatus for achieving the aboveobjects utilizing vacuum as the sole degassing agent which will enablethe metal to be degassed within its permissible temperature droplimitation.

Another object is to provide a new and improved ladle for degassingsmall heats of molten metal.

Another object is to provide a vacuum degassing assembly which includesa ladle assembly and a unique hood covering the upper surface of themelt to thereby reradiate heat back to the melt, or, in other words,conserve the heat of the steel in the ladle assembly.

Other objects and advantages will become apparent from a study of thefollowing specification and claims.

My invention is illustrated more or less diagrammatically in theaccompanying iigures wherein:

FIGURE 1 is a side elevation with portions broken v away;

FIGURE 2 is a front elevation taken substantially along the line 2-2 ofFIGURE 1;

FIGURE 3 is a top view taken substantially along the line 3-3 of FIGURE1 with portions omitted for clarity; and

FIGURE 4 is a side view of my degassing unit positioned within a vacuumtank.

Like reference numerals will be used to refer to like parts throughoutthe following ldescription of the drawings.

In FIGURE 1 my degassing assembly is indicated genera-lly at 10. Itincludes a lower portion which is essentially a ladle 11 and an upperportion 12 which acts as a radiation shield and enables almost the fulldepth of the ladle to be utilized as explained hereinafter. As can -beseen in any one of FIGURES 1, 2 and 4, the de- Vgassing unit isessentially barrel shaped. A stopper rod is yindicated generally at 13and a stopper rod rigging at 14. In this instance a bottom Iladle hasbeen illustrated but the invention is not limited to this type of ladle.A 4lip pour or teapot ladle could also be used.

The wall of ladle 11 consists essentially of an outer steel shell 15 andan inner lining 16 of refractory may be used and the thickness may varyanywhere from 4 to 5 inches, or perhaps more or less, depending to someextent on the size of the ladle and the requirements at a `giveninstallation. A ybottom plate 17 is welded about its periphery to thelower `edge of steel shell 15. A skirt 18 is welded to plate 17 to forma support for the degassing unit.

The walls of the lowe-r portion diverge slightly outwardly in an upwarddirection as can 'best be seen in FIGURES l, 2 and 4. A plurality ofradially outwardly directed U-shaped lugs 20, 21, 22 and 23 are weldedto the steel shell 15 at the point of maximum circumference. The uppersurfaces of t-he lugs are coplanar with the upper surface of the walls,and the lugs are equally spaced one from another.

A band 25 is secured to the exterior of the ladle. A pair of trunnionplates 26, 27 `are bolted to the band 25. Each trunnion plate includes atrunnion journal 2S, 29 which receives a trunnion 30, 31, respectively.

The upper portion 12 of the degassing unit has the shape of a lopsidedfrustum of a cone. The wall construction of the upper section isstructurally similar to the ladle portion in that it consists of anouter shell 33 to Which a suitable 'layer of refractory, not shown, issecured. The upper section terminates at its upper end in a flange 34and at its Ilower' end in a connecting ange 35. Slots 36 in flange 35overlie the slots in lugs 20-23.

Suitable connecting bolts, not shown, secure ange 35 to lugs 20-23 tothereby connect the upper .and lower sections.

'Ihe slope of the walls of upper section 12 varies from a maximum at 38to a minimum in the wall section area designated generally at 39.

The provision of a sloped wall surface is especially advantageous inreducing lrefractory drip. `It appears that the inclined surface retainsor absorbs less heat than does a flat surface .and consequently theillustrated configuration is more advantageous than a flat dis-c locatedat the level of ange 35. The radiation shield or skirt 12 Iis thereforean important feature in the conservation of heat during the degassingprocess. The provision of a relatively tlat refractory surface at anelevation considerably above the level of flange 35, such as closuremember 64, is acceptable since the intensity of the radiant heat Varieswith the square of the distance from the source and accordingly theproblem of refractory drip is not so acute at the higher elevation.

The provision of a sloped or upwardly and inwardly extending wallsurface in the region next adjacent the top of the ladle is also ofgreat advantage `from the standpoint of ladle maintenance. Since thelevel of the molten metal may 'be very close to the top of the ladlesome metal may be deposited on the upwardly and inwardly extendingsurface. The sloped surface makes stripping of the deposited meta-l arelatively simple task as compared to refurbishing a flat surface.

A tapping opening 40 is cut in the area of minimum slope. By locatingthe tapping opening 40 in the wall section of :minimum slope, a tappingopening of maximum horizontal area is provided vfor a ,given area ofopening.

A removable door is indicated generally at 42. The door consistsessentially of a flat plate 43, a depending sheet 44 which is contouredto make snug engagement with the wall section 39, and a suitable layerof refractory 45. An inverted U-shaped frame y46 is pivoted about a rod47 which in turn yis journaled `in a pair of pivot plates 48, 49 weldedto flange 35. Frame 46 carries a pivot rod 50 which is received in apair of plates 51, 52 projecting outwardly from plate 43. In order toprevent the door from revolving about pivot rod 50 when it is swungclockwise to permit molten metal to be poured into the ladle, a stop `53is welded to the upper end of the door supporting Iframe 46. A stop bar53a welded to the outer llower edge of pivot plates 48, 49 prevents theframe 46 from swinging downward against the ladle.

The black head 54 of stopper rod 13 seats in a discharge nozzle 55located in a pouring opening in the -bottom of the lad-le. Any suitablemeans maybe provided for securing the nozzle to the ladle. In thisinstanoe, a plate 56 has been bolted to a ring 57 welded to the bottomplate 17. The plate 56 bears against a shoulder in nozzle 55.

The stopper ro-d -rigging 14 may be of any conventional design. As canbe observed from FIGURE l, a conventional tipping rigging has beenmodified to the extent that the rod may only ibe move-d up and down. Inother words, by rotating handle 58 vertical rod 59 is raised andlowered. Supporting arm `60 is bolted to -rod 59 at its inner end andthreadably connected to stopper core rod 61 at its outer end. Rotationof handle 5S thereby seats and unseats the nozzle.

The upper end of Ithe section 12 is apertured as at 63 to permit entryof the stopper rod 13. The stopper rod carries a radiation plate 64which consists essentially of a flat circular plate 65, a dependingskirt 66 welded thereto, and a layer of refractory material 67 securedto plate 65. As can best be seen in FIGURE l, radiation plate 64substantially overlaps opening 63. It is spaced a few inches away fromthe opening to thereby provide a gas escape passage 68 for gases givenolf by the molten metal in the ladle 11.

The use and operation of my invention are as follows: In order to degasa heat of molten metal, a stopper rod 13 is rst seated on the nozzle 55.Door 42 is then swung open and the degassing unit positioned to receivemetal from a furnace or other source of supply. Molten metal is thenadmitted to the degassing unit. At A, B and C I have indicated moltenmetal levels for 2,121/2, and 3% tons of steel.

After the-desired amount of steel is tapped into the ladle, door 42 isswung shut. tion plate 64 in place, the upper section 12 forms, in

elect, a substantially continuous radiation shield 'over the surface lofthe exposed metal. Since a substantially continuous hood or shell ofrefractory is provided, heat loss from the upper surface of the meta-lis kept at a minimum. It is desirable that radiation plate 64 overlapthe opening 63 in order to prevent any radiant heat from passingunobstructedly out of the ladle.

The degassing unit lis then placed in the vacuum cham-r ber indicatedgenerally at 70 in FIGURE 4. It will be understood that the degassingunit will be transferred by bail 71 which is locked in the positionshown in FIG- URESZ and 4 by handle 72.' The inner end of handle 72 isreceived in a slot formed in dog 73 welded to flange 35. The vacuum tankis large enough to clear the bail 71. The tank is shown in closedposition by dotted lines 74 in FIGURE 4. In this instance, a clam shelltype vacuum tank has been illustrated. Essentially the tank` consists ofa stationary half 75 and a movable half 76` which swings about pivot 77.A cylinder and piston arrangement 78, 79 operated yby hydraulic fluidfroml a source, not shown, opens and closes the tank. A vacuum is drawnthrough conduit 80. The degassing operation can be observed through thewindow 81. The two halves of the clam shell tank carry sealing flanges82, 83 which, when in engagement, form an air-tight se-al which enablesa vacuum on the order of l millimeter of mercury or;

less to be drawn in the tank.

At the conclusion of the degassing operation, the tank is opened. If alarge number of small castings are to` z be poured, a synthetic orine-rt slag may be added to the` degassed melt in order to conserve heatbetween the end of the degassing operation and the end of the pouringoperation. By inert or synthetic slag, I mean -a slag which will notgive olf to the heat deleterious gases similar to those drawn olf lbythe degassing operation. My apparatus therefore enables the melt to bedegassed withouta slag blanket. The presence of a slag blanket during idegassing would lengthen the degassing cycle and hinder the degassing.As a result, stratification of the metal may occur.

The unique construction of the upper section or radiation shield isespecially important to the excellent results obtainable from mydegassing unit.

In the first place, the radiation shield, which might be` it wouldalways be at a temperature considerably below that of the molten metal,a large temperaturedifferential would exist and loss by heat transferwould be excessive.

By lining the outer metal shell 33 with refractory, the

temperature differential between the metal and hood `is reduced. tozero, or close to it, since the refractory will heat to, or close to,the temperature of the molten metal. In addition, the refractoryprotects the metal shell 33 from the heat of the melt.

In the second place, the heat conservation shield is as small bulkwise,i.e., volume, as it can be. Therefore,

With door 42 and radiathe amount of heat lost due to absorption by theshield is at a minimum. It will vbe noted that upper section 12 at itswidest point is only as wide as the upper end of the ladle 11. Theinwardly, roughly parabolic-shaped contour is the smallest bulk ofmaterial that can be utilized consistent with providing boil clearance.Loss by heat absorption accounts for much of the heat lost otherwisethan by transference through the hood.

In the third place, the heat shield enables theladle 11 to be lled to ahigher level than any comparable ladle I am aware of that is used invacuum degassing. Note, for example, line C in FIGURE l. Without theheat shield, the ladle could only be filled to approximately the Alevel, or perhaps even below. This is because the boil in the ladlecreated by the vacuum throws metal up approximately two feet above thesurface in a ladle similar to that shown in the drawings. Without theheat shield, the boil would throw metal out of the ladle if the moltenmetal level is at C. With the heat shield, the ladle can readily befilled to level C since the boiling metal will splash against therefractory, which -is at substantially the same temperature as thesteel, and fall back into the ladle. A flat shield could not be used ofcourse as it would provide no clearance for the carbon monoxide boil.

This increased capacity of the ladle is of particular importance to thesmall foundry man who pours a wide range of sizes of castings. With a31/2 ton ladle, for example, he may be able to pour 3 to 3% tons ofmetal so that two 11/2 ton castings could be poured in one heat. Withoutthe hood, only 2 to 21/2 tons lof metal could be handled, 4and thus onlyone 11/2 ton casting could be poured per heat. The heat conservationshield therefore, in effect, doubles the foundry mans capacity.

Actual nal included gas contents of l.l p.p.m. H2, 23 p.p.m. N2, and 25ppm. O2 have been achieved in approximately 5,000 pound heats tapped ataround 3,120 degrees F. and degassed for approximately 5 minutes. Totalelapsed time from start tap to teem has varied from 14 to 23 minutes.Total elapsed times of 14 to 16 minutes have been consistently achieved.The aforementioned times are well within the permissible temperaturedrop limitation of the steel degassed. The steel had a nominalcomposition of C .S0-.60, Mn .G5-.90, Si .20- .35, Ni .80-1.00, Cr.S0-1.10, Mo .2S-.35.

Although a preferred embodiment has been illustrated and described, itwill be understood that the invention is not so limited in application.Accordingly, the scope of the invention should only be limited by thescope of the hereinafter appended claims.

I claim:

1. A degassing unit for lowering the included gas content in commercialsized baths of molten steel within the permissible temperature droplimitation of the steel, said degassing unit including a ladle and aradiation shield assembly carried by and overlapping the ladle tothereby form a substantially uninterrupted heat radiating surface overthe ladle, the interior lining of the shield being cornposed of arefractory material, said radiation shield assembly having walls whichconverge upwardly, inwardly from the upper end of the ladle to therebyprovide a radiation shield for conserving the heat of the steel in theladle, said Walls converging upwardly, inwardly non-uniformly to therebyprovide a wall section of minimum slope as contrasted to the balance ofthe wall, said wall section of minimum slope having a tapping openingtherein whereby molten steel may be admitted to the ladle, a cover forthe tapping opening pivoted on the degassing unit, said cover, when inposition covering the tapping opening, forming a portion of thesubstantially continuous heat radiating surface, a stopper rod carriedby radiation shield assembly, and a radiation plate carried by andremovable with the stopper rod, said radiation plate overlying anopening in the radiation shield through which the stopper rod passes andbeing out of contact therewith at all times Y to thereby provide a gasescape passage for gases given olf from the molten steel in the ladle,said radiation plate forming a portion of the substantially continuousheat radiating surface.

2. The degassing -unit of claim 1 further characterized in that theradiation shield assembly, at its widest point, is substantiallyco-terminous with the upper end of the ladle and is in operative contactwith the upper end of the ladle whereby the heat storage capacity of theradiation shield assembly is at a minimum.

3; An apparatus for lowering the included gas Vcontent in commercialsized baths of molten metal within the permissible temperature droplimitation of the metal, said apparatus including a receptacle havingstructure defining a gas escape passage therein discharging externallyof the receptacle wall for the exit of gases removed from a bath ofmolten metal contained within the receptacle, said structure comprisinga radiation assembly externally spaced from and peripherally overlappingthe gas escape passage, the upper portion of said receptacle converginginwardly, upwardly from a point in the vicinity of the highest moltenmetal level to thereby provide a rellecting shield for conserving theheat of the bath during tapping and treatment, one wall section of theupper portion of said receptacle having a tapping opening therein forthe reception of a removable tapping cover, which, when in positioncovering the opening, provides a substantially continuous radiationshield, said opening being of a size suicient to provide easy access tothe interior of the receptacle to thereby facilitate filling thereof,and means for discharging degassed molten metal from the receptacle.

4. The vacuum degassing apparatus of claim 3 further characterized inthat the upper portion of the receptacle converges inwardlynon-uniformly to thereby provide a wall section of minimum slope, thetapping opening being located in said wall section of minimum slope tothereby provide maximum tapping access to the interior of the receptaclefor a given opening area.

5. The vacuum degassing apparatus of claim 3 further characterized,firstly, in that the means for discharging molten metal from thereceptacle includes a stopper rod seated in a discharge opening in thebottom of the receptacle, and, secondly, in that the radiation assemblyincludes a radiation member, said stopper rod carrying the radiationmember, said radiation member being spaced from an opening in thereceptacle to thereby form the gas escape passage between the radiationmember and the receptacle, said radiation member thereby forming aportion of the continuous radiation shield over the molten metal.

6. An apparatus for lowering the included gas content in commercialsized baths of molten metal within the permissible temperature droplimitation of the metal, said apparatus including a receptacle havingstructure defining a gas escape passage therein discharging externallyof the receptacle wall for the exit of gases removed from a bath ofmolten metal contained within the receptacle, and said structurecomprising a radiation assembly externally spaced from and peripherallyoverlapping the gas escape passage, the upper portion of said receptacleforming a shield for conserving the heat of the bath during tapping andtreatment, one wall section of the upper portion of said receptaclehaving a tapping opening therein for the reception of a removabletapping cover, which, when in position covering the opening, provides asubstantially continuous radiation shield, said opening being of a sizesufcient to provide easy access to the interior of the receptacle tothereby facilitate filling thereof, and means for discharge degassedmolten metal from the receptacle.

7. A radiant heat loss reduction assembly for use with a molten metalcontaining receptacle such as a vacuum degassing treatment receptacle,said assembly comprislng a generally upwardly and inwardly extendingwall 7` structure, the inclination of which commences substantially atthe lower edge portion thereof, said wall structure having a generallycircular horizontal cross section at any vertical location, the largesthorizontal cross section occurring at the lower edge portion, thesmallest horizontal cross section occurring at the upper edge portion,said upper edge portion terminating in an open outlet, the periphery ofwhich lies in a horizontal plane, and an associated cover memberoverlying said upper edge portion, said cover member being spaced aboveand out of contact with the said upper edge portion. 8. The radiant heatlosslreduction assembly of claim 7 further characterized in that atleast a portion of the central area of the cover member is substantiallyhorizontal, said central area being located furthest away. in a verticaldirection from the lower edge portion of the wall structure,

References Cited by the Examiner UNITED STATES PATENTS FOREIGN PATENTS11/1950 Canada.

4/1941 Germany. i

OTHER REFERENCES Modern Castings, page 7, July 1960.

JOHN F. CAMPBELL, Primary Examiner.

WHITMORE A. WILTZ, J. M. ROMANCHIK,

Assistant Examiners.

1. A DEGASSING UNIT FOR LOWERING THE INCLUDED GAS CONTENT IN COMMERCIALSIZED BATHS OF MOLTEN STEEL WITHIN THE PERMISSIBLE UNIT INCLUDING ALADLE AND A RADIATION SHIELD DEGASSING UNIT INCLUDING A LADLE AND ARADIATION SHIELD ASSEMBLY CARRIED BY AND OVERLAPPING THE LADLE TOTHEREBY FORM A SUBSTANTIALLY UNINTERRUPTED HEAT RADIATING SURFACE OOVETHE LADLE, THE INTERIOR LINING OF THE SHIELD BEING COMPOSED OF AREFRACTORY MATERIAL, SAID RADIATION SHIELD ASSEMBLY HAVING WALLS WHICHCONVERGE UPWARDLY, INWARDLY FROM THE UPPER END OF THE LADLE TO THEREBYPROVIDE A RADIATION SHIELD FROM CONSERVING THE HEAT OF THE STEEL IN THELADLE, SAID WALLS CONVERGING UPWARDLY, INWARDLY NON-UNIFORMLY TO THEREBYPROVIDE A WALL SECTION OF MINIMUM SLOPE AS CONTRASTED TO THE BALANCE OFTHE WALL, SAID WALL SECTION OF MINIMUM SLOPE HAVING A TAPPING OPENINGTHEREIN WHEREBY MOLTEN STEEL MAY BE ADMITTED TO THE LADLE, A COVER FORTHE TAPPING OPENING PIVOTED ON THE DEGASSING UNIT, SAID COVER, WHEN INPOSITION COVERING THE TAPPING OPENING, FORMING A PORTION OF THESUBSTANTIALLY CONTINUOUS HEAT